Articulated tool for drilling oil, gas geothermal wells

ABSTRACT

The invention relates to a tool for drilling oil, gas or geothermic wells. The tool includes two main members, a hollow shaft (1) and a blind tool body (2) more elongate than conventional tool bodies; the two main members are spherically connected to each other by means of a ball joint (4,5). The ball joint is located at the very bottom of the blind portion of the tool body which carries a stabilizer (19) at the other end. The tool is also provided, between the hollow shaft and the tool body, with an appropriate transmission system (6, 7, 8, 9, 11), which is spaced apart from the ball joint and situated between the latter and the stabilizer. The essential advantage of the tool lies in the relative position of the ball joint and the stabilizer, the positioning conferring on the tool a favorable dynamic behavior, without risk of buttressing. Field of application: drilling of oil wells, gas wells and geothermic wells.

BACKGROUND OF THE INVENTION FIELD OF THE INVENTION

The intention relates to a tool for drilling oil, gas or geothermalwells, driven in rotation either from the surface by a rotating systemof drill rods and collars, or by an underground engine.

SUMMARY OF THE INVENTION

The tool is comprised of two main components. The first is a hollowshaft which is connected by one of its ends either to the last rod inthe column, or to the shaft of the engine through which the drilling mudmust be led. In either case, for purposes of unity of language, the rodor the shaft of the engine to which the hollow shaft belonging to thetool is connected will be called the "driving element." It is alsothrough this driving element that the forward thrust is transmitted tothe tool. The second main component of the tool is a blind tubular body,hereinafter called the "tool body," the closed end of which externallycarries the cutting edges, and the open end of which allows the passageof the hollow body.

The main components are spherically connected, and this connection isprovided by a ball joint; the common center of the two sphericalsurfaces that it places in contact is called the "center of the balljoint". The-existence of this spherical connection requires the use of asecond connection which allows the drilling torque to be transmittedfrom the hollow shaft to the tool body while maintaining the relativeclearances of these two components stemming from their sphericalconnection.

An articulated tool which corresponds to this definition exists in theprior art (patent GB-A-2.190.411). The tool described by this patent isdesigned for use in deviated drilling; because of this, the tool body isas short as possible, the ball joint is located above the tool body(GB-A-2.190.411), the hollow shaft is almost entirely outside the toolbody and the transmission system is integrated into the ball joint, tothe detriment of the area of the spherical contact surfaces.

The tool which is the subject of the present invention is preferablyintended for drilling in a straight line. This tool has a relativelyslender body, the ball joint is located at the very bottom of the blindend of the tool body, which carries a stabilizer at its other end, andthe transmission system, which is separate from the ball joint, islocated on the same side of this ball joint as the stabilizer. Thedistance between the center of the ball joint and the stabilizer, ormore precisely between this center and the plane perpendicular to theaxis of the tool situated at the mid-height of this stabilizer, must beat least on the order of 2.5 times the diameter of the tool body, andeven greater when the lateral aggressiveness of the cutting edges of thetool is greater.

The transmission systems used in the tool which is the subject of theinvention are distinguished from those used in the known articulatedtools by the fact that they are outside the ball joint, and thus avoidreducing its supporting surfaces, and by the fact that they comprise,between the hollow shaft and the tool body, an intermediate elementwhich surrounds the hollow shaft. This element is connected to each ofthe main components by a particular toothing when this element is rigid,or by a joint when it is deformable (flexible shell). In any case, it iscalled a "variable configuration" transmission.

Any comparison between the behavior of the tool which is the subject ofthe invention and the articulated tools cited in the prior art isdifficult, since their preferred fields of application are different.

As compared to the known monolithic tools, the advantages offered by thetool which is the subject of the invention reside in its dynamicbehavior. This behavior is rendered largely independent from theparasitic movements of the driving element, without this independencepreventing the tool itself from reacting to the most troublesomevibrations caused by the cutting movement and without allowing its twomain components to enter into a buttressing configuration. Theseadvantages result from the relative position of the ball joint and thestabilizer belonging to the tool body.

Two possible cases of operation of the tool which is the subject of theinvention will be considered.

In the first of these cases, it is assumed that the axis of the hollowshaft joined to the driving element is maintained by the latter alongthe axis of the well already drilled and that the tool, as a result ofthe cutting conditions it encounters, tends to begin a precessionmovement. The position of the center of the ball joint, with which thevertex of the precession cone is identified, allows the tool body toreact spontaneously to the resultant inclination of the cutting force;this force itself tends to bring the tool body into coaxiality with thehollow shaft, with a sensitivity that increases the further the centerof the ball joint is located from the contact surfaces of this balljoint, in the direction of the forward movement of the tool. In thiscase, the action of the stabilizer prevents the relative inclination ofthe tool from becoming enough to create a contact between the hollowshaft and the tool body at the open end of the latter before thespontaneous reaction of the tool has occurred.

In the second case considered, a deformation of the driving element isassumed to cause the axis of the hollow shaft to be inclined relative tothe axis of the well. In this case the axis of the hollow shaft relativeto the axis of the well describes a cone, the vertex of which coincideswith the center of the ball joint. The tool body tends to follow thehollow shaft in this movement, but the stabilizer prevents it from doingso, in a way that is particularly effective if the stabilizer is inrotoid connection with the tool body: the latter then continues toprogress along the axis of the well, independently from the disturbedmovement that the deformed driving element is imposing on the hollowshaft.

The position of the ball joint at the very end of the tool body makes itpossible to place the center of this ball joint as far away as possiblein the direction of the forward movement without excessively weakeningthe lateral guiding power of the spherical connection. But thisspherical connection becomes unilateral, and an alternate contact musttherefore be provided between the two main components of the tool inorder to allow the tool to be lowered and raised without the risk oflosing the body.

By thus placing the center of the ball joint as far away as possible inthe direction indicated, the dynamic behavior of the tool is improvedand the distance between the center of the ball joint and the stabilizeris increased for a given slenderness of the tool body.

When the contact surfaces in the ball joint and in the transmissionsystem are metallic, lubrication of these surfaces is essential not onlyfor their preservation, but in order to reduce friction stress in thesecontacts, which can cause the behavior of the tool to deviate from itsideal behavior. Therefore, if necessary, it is possible to isolatebetween the tool body and the hollow shaft a lubricating chamber whichcontains the ball joint and the variable configuration transmissionsystem. This chamber is limited by a deformable double seal system whichenables the relative movements of the tool body and the hollow shaftallowed by the ball joint and makes it possible to maintain the enclosedlubricant at a pressure near that of the flow of drilling mud risingtoward the surface.

BRIEF DESCRIPTION OF THE DRAWINGS

The sole FIGURE shows, by way of a non-limiting example, a drilling toolaccording to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The partial section presented in this FIGURE shows the two maincomponents which constitute the tool: the hollow shaft 1 and the toolbody 2 in a blind tubular shape, which carries at its closed end thecutting-tips such as 22. The hollow shaft 1 is joined at one of its endsto the driving element, not represented, by means of the tapered thread3. At its other end, the hollow shaft 1 is spherically connected to thetool body 2 by a ball joint, located in the closed end of the tool bodyand constituted by the element 4 which carries the male surface and isintegral with the tool body as well as by the element 5 which carriesthe female surface and is integral with the hollow shaft. The male andfemale contact surfaces, which are in conformity in the ball joint, arecentered on the point A which is called the center of the ball joint.The hollow shaft 1 and the tool body 2 are also connected by the sleeve6 which has an internal spur toothing 7 and an external rounded toothing8. The internal spur toothing 7 of the sleeve meshes with the externalrounded toothing 9 with the same number of teeth, machined on the part10 integral with the hollow shaft, and the external rounded toothing 8of the sleeve meshes with the internal spur toothing 11, with the samenumber of teeth, integral with the tool body. This second connectionbetween the hollow shaft and the tool body therefore exists in the formof a deformable coupling, the sleeve 6 having am additional pointcontact through the surface 12 with the part 5 of the ball joint, so asto limit toward the front the absolute translation of the sleeve.

Since in this case the spherical connection produced by the ball joint4, 5 is unilateral, that is apt to transmit from the hollow shaft to thetool body a thrust which acts only in the direction of the forwardmovement, a substitute contact is provided between the surface 13 linkedto the hollow shaft and the surface 14 linked to the tool body duringthe lowering or the raising of the tool in order to allow, during theseoperations, the transmission of a thrust which acts from the hollowshaft to the tool body in the direction opposite that in which the balljoint can transmit.

Two sealing systems, which respectively use the membranes 15 and 16,isolate from the drilling mud, between the hollow shaft and the toolbody, an oil chamber 17 containing the lubricant essential to the balljoint and to the coupling.

The membrane 15 (front membrane), which in the free state has the shapeof a tube carrying a flange at one of its ends, is engaged by itstube-shaped part in the internal surface of the hollow shaft and by itsflange-shaped part in the tool body. This membrane, which separates thedescending mud flow (at high pressure) from the lubricant contained inthe oil chamber, conforms to metal surfaces over the largest part of itsarea, and is free on an area of its surface just large enough for it tohave the necessary deformability for the relative clearance of thehollow shaft relative to the tool body during the operation of the tool,and during its raising or lowering, so as to allow the surfaces 13 and14 to come into contact.

The membrane 16 (rear membrane), which in the free state has the shapeof a truncated cone, is attached by the perimeter of its small base tothe external surface of the hollow shaft, and by the perimeter of itslarge base to the internal surface of the tool body, in such a way thatthe small base is situated on the side of the open part of the toolbody. Lateral openings such as 18 are cut into the tool body, at theheight of the membrane 16, in order to lead to this location the risingmud flow inside the tool body, and thereby to create, along the rearsurface of the membrane, a sweeping effect which prevents anysedimentation of hard bodies in proximity to this membrane.

The tool comprises a stabilizer 19 near the open end of the tool body.In the embodiment illustrated here, this stabilizer 19 is in rotoidconnection with the tool body by means of rolling bearings 20 and 21,lubricated separately with grease during assembly and maintenance.

I claim:
 1. A tool for drilling oil, gas or geothermal wells, driven inrotation by a driving element which also transmits to it a forwardthrust, constituted by two main components, one of which is a hollowshaft joined by one of its ends to the driving element, and the other ofwhich is a blind tubular body, here called the tool body, the closed endof which externally carries the cutting edges and the open end of whichallows the passage of the hollow shaft, in which the two main componentsare spherically connected, characterized:in that the hollow shafttransmits the drilling torque to the tool body through a transmissionsystem called a variable configuration transmission system comprising,between the hollow shaft and the tool body, an intermediate elementconnected to each of the main components, in that a ball joint whichembodies the spherical connection is located at the very bottom of theblind part of the tool body, in that the tool body carries a stabilizerlocated at its other end, at a distance from the center of the balljoint on the order of at least 2.5 times the external diameter of thetool body, in that the variable configuration transmission system isseparate from the ball joint and located on the same side of this balljoint as the stabilizer and in that this system uses, to transmit thedrilling torque, the intermediate element and wherein the intermediateelement surrounds the hollow shaft.
 2. The drilling tool according toclaim 1 characterized in that the spherical connection located at thebottom of the tool body is unilateral so that it only transmits, fromthe hollow shaft to the tool body, a thrust acting in the direction ofthe forward movement, the center of the ball joint thus being able to beplaced as far away as possible in the direction of the forward movement.3. The drilling tool according to claim 1, characterized:in that thevariable configuration transmission system is constituted by a sleevecontained in the tool body, which carries at one of its ends an internalspur toothing and at the other end an external rounded toothing, in thatthe internal spur toothing of this sleeve meshes with an externalrounded toothing, with the same number of teeth, integral with the toolbody and in that the external rounded toothing of the sleeve meshes withan internal spur toothing, with the same number of teeth, integral withthe tool body, so as to constitute a deformable coupling between thehollow shaft and the tool body, an additional point contact of thesleeve on one of the main components of the tool unilaterally limitingthe absolute translation of the sleeve without thereby restricting therelative clearances.
 4. The drilling tool according to claim 1,characterized in that the stabilizer located near the open end of thetool body is in rotoid connection with the tool body.
 5. The drillingtool according to claim 1, characterized in that a deformable doubleseal system isolates, between the hollow shaft and the tool body, an oilchamber which contains the ball joint and a transmission joint, and inthat this double seal system is constituted by a front membrane, whichin the free state has the shape of a tube carrying a flange at one ofits ends, the tube-shaped part of this membrane being engaged in aninternal surface of the hollow shaft and the flange being engaged in thetool body, and a rear membrane, which in the free state has the shape ofa truncated cone and which is attached in an external surface of thehollow shaft and in the internal surface of the tool body, in such a waythat the small base of the truncated cone is located on the side of theopen part of the tool, andin that the tool body, at the height of therear membrane, has openings which allow the rising mud flow to be ledinside the tool body, creating along the rear membrane a sweeping effectwhich prevents the sedimentation of hard particles between the rearmembrane and the tool body.